The present invention relates to a drive shaft assembly, a rail adjustment system with a drive shaft assembly and a method of manufacturing a drive shaft assembly.
A generic drive shaft assembly has at least one flexible drive shaft for transferring an adjustment force and an elongate guide. The flexible drive shaft thereby comprises a central part extending between the two shaft ends of the drive shaft, which is at least partially arranged in the elongate guide. The physical guide for the flexible drive shaft is for example formed by a flexible guide tube into which the central part is inserted, and/or by a guide channel in a retaining element which mounts the flexible drive shaft in a rotational manner.
Such a drive shaft assembly is for example part of a drive of a rail adjustment system for a vehicle seat in order to displace the vehicle seat in a longitudinal seat direction. For this, the rail adjustment system typically has two pairs of rails, where respectively a first rail is mounted relative to a second rail in a longitudinally displaceable manner, and the two first rails are adjustable together relative to the two second rails of the rail pairs by means of a drive device of the rail adjustment system. The flexible drive shaft of the drive shaft assembly is hereby arranged at a typically plate-shaped retaining element that is fixed to the two first rails. The flexible drive shaft is driven at one shaft end by a drive motor of the drive device, for a rotation around its shaft axis and is, at its other shaft end, in operative connection with a spindle drive at one of the two rail pairs. The flexible drive shaft is for example coupled to a spindle gear having a pivot-mounted spindle nut, and, when rotating the flexible drive shaft, is driven for a rotation around a fixed spindle axis. By means of the rotation of the spindle nut, the spindle gear moves along the spindle axis of the spindle and thereby is the first rail connected to the spindle gear relative to the second rail holding the spindle. In parallel, the first rail of the other rail pair is displaced relative to its second rail. Such a rail adjustment system with a drive shaft assembly is for example known from DE 10 2007 027 322 A1. In addition, US 2001/00 52 721 A1, US 2005/01 21 586 A1 and WO 92/08061 A1 show comparable drive shaft assemblies.
It is known in particular from the above-mentioned specifications to provide flock fibers at a flexible drive shaft or at a guide for the drive shaft, and thereby to provide a flocking within the scope of the manufacturing process of a drive shaft assembly. For example, the central part extending between two shaft ends of a flexible drive shaft which is arranged within a guide, e.g. a flexible guide tube is provided evenly with flock fibers in order to reduce a play between the guide and the drive shaft in the region of the central part, and to avoid the generation of noise during a rotation of the flexible drive shaft by means of abutting or rubbing against an inner surface of the guide.
In practice it has however been shown that undesired noise and vibrations can occur during a rotation of the drive shaft with an increased operating time, as the flock fibers are compressed over time. In particular, with rail adjustment systems for a vehicle seat it has been observed that, within the expected life span of the drive shaft assembly, measurable and possibly even noticeable vibrations and audible noise can occur when the vehicle seat is adjusted by means of the rail pairs of the rail-adjustment system along the longitudinal axis of the seat. Due to the relatively high rotational speeds of the flexible drive shaft, a buzzing sound can possibly be heard, for example, when the drive shaft rotates, and is already in use for some time.
From EP 1286065 A1, a wound flexible drive shaft is known, in which a flocked wire is used for an outer winding. The single flocked wire is spirally wound around the shaft axis of the drive shaft and is placed into a circumferential gap in the outer winding. The production of such a flexible drive shaft with flock fibers requires in particular a previous production of a flocked single wire and an adaptation of the winding process for the manufacture of the drive shaft, and therefore appears relatively elaborate and expensive.